In recent years, a swallowable capsule endoscope has been developed in the field of an endoscope. The capsule endoscope having an imaging function and a radio communication function is inserted from a mouth into a body of a subject for an observation, and travels to capture images of the inside of organs such as the stomach, the small intestine, and the large intestine according to their peristalsis until it is naturally excreted.
While the capsule endoscope travels inside the organs, image data captured by the capsule endoscope in the subject body is sequentially transmitted to the outside of the subject by a radio signal to be stored in a memory provided in a receiver placed outside of the subject, or displayed on a display provided to the receiver. A doctor, a nurse, or the like can make a diagnosis based on images displayed on a display based on the image data stored in the memory, or images displayed on the display provided to the receiver simultaneously with the receiver's data reception.
Since the number of a series of images captured by the capsule endoscope is usually enormous, the doctor, nurse, or the like needs a great amount of time and effort to observe the enormous number of images and make a diagnosis. In response to such a circumstance, an image display apparatus, which has an improved image search performance and enables an easy recognition of what organ the image on the display captures, has been proposed (see Patent Document 1, for example).
The image display apparatus displays a time scale which indicates an imaging period of the series of images, and also displays time-series average colors of respective images on the time scale. Since the average colors of the images correspond to captured-organ-specific colors, respectively, the doctor, nurse, or the like can easily recognize, by observing the average color displayed on the time scale, what organ the images at respective imaging time points capture.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-337596